1. Field of the Invention
The present invention relates to a lamp temperature control device, and a color direct thermal printer having the control device. More particularly, the present invention relates to a lamp temperature control device capable of maintaining intensity of radiation of the tubular lamp while adjusting tube temperature of the tubular lamp.
2. Description Related to the Prior Art
There are various machines including tubular light source such as a fluorescent lamp or an ultraviolet lamp. In a color direct thermal printer, an ultraviolet lamp in a tubular shape is used to emanate ultraviolet radiation for fixing one of primary color images recorded on color thermosensitive recording material. The color thermosensitive recording material is constituted of base sheet, a cyan coloring layer, a magenta coloring layer, and a yellow coloring layer. The thermal recording is performed in the order from an uppermost layer at the obverse to the undermost layer. The coloring of a layer, of which the recording is finished, is fixed by application of ultraviolet radiation in a wavelength range appropriate for each layer, before the next underlying layer is subjected to the recording. This is for the purpose of invalidating the coloring ability and preventing the colored layer from being colored by next heating. Since the ultraviolet lamp emanates radiation not only to the front but also to the rear, a reflector is disposed behind the lamp.
The ultraviolet lamp, as disclosed in JP-Y 63-33321, has a radiating intensity which is changeable according to the temperature of a lamp tube. The lamp has such characteristics that, if the tube temperature is lower, then the radiating intensity is lower; if the tube temperature rises, then the radiating intensity is raised; and when the tube temperature is extremely high, then the radiating intensity decreases. In view of stabilizing the fixation of the coloring, it is necessary to keep constant the ultraviolet radiating intensity, without being influenced by changes in the tube temperature of the lamp.
In the conventional thermal printer according to the color direct recording, there is provided a sensor for detecting temperature and a lamp cooling fan, in order to control the radiating intensity of the lamp, so that the tube temperature of the lamp is kept from being high. The fan is disposed in association with the one end of the lamp and applies with cooling air from the one end toward the other end. The lamp is somewhat long in order to direct a center portion of the lamp to a recording area of the recording material, since the center portion of the lamp has large and stable radiating intensity.
However, it is difficult to apply such long lamp overall with the cooling air from the one end to the other end of the lamp, so that the long lamp has different tube temperature between a position near the fan and a position apart from the fan. That causes the color recording material to be supplied with uneven intensity ultraviolet radiation depending on the directed portion of the long lamp, and unstable color fixation to be occurred.